NEW 7" REELS OF • *. GI.dlOtape gIve you EXTRA VALUE at no ·extra cost! GUARANTEED SPLICE-FREE _. ________ SPLIT-SECOND TIMING with New 2%:" Hub Timing errors are virtually eliminated by this improved reel design which minimizes tensio n and speed changes throughout the winding cycle. Ratio of D.D. to hub diameter is the same as on the standard NAB aluminum reel. PERFECTED ANTI- FRICTION With Audiotape, all of these extra-value features are standard. There's no extra cost - no problem of separate inventories or­ PROCESS. Reduces head wear-eliminates variations in tape quality. annoying tape "squeal" - prevents "tackiness" F or there's only one Audiotape - the fin est obtainable anywhere. even under extreme temperature and humidity Test it - compare it -let Audiotape speak for itself. conditions. The new 7-inch plastic reel with large diameter hub for greater timing accuracy is now being supplied on all orders unless other­ wise specified. Because of increased hub diameter, maximum reel MAXIMUM UNIFORMITY OF capacity is slightly over 1200 feet. Older style Audiotape reels 3 OUTPUT. All 7" and 10" reels of plastic· with 1 ,1,," hub and 1250 feet of tape will continue to be furnished on request at the same price. base Audiotape are guaranteed to have an out·, * Trade Mark put uniformity within ± lJ.. db - and reel-to· reel-variation of less than ± 1/2 db. What's more, there's an actual output curve in every S-reel package to prove it. AUDIO DEYICES, Inc. 444 Madison Ave., New York 22, N. Y. Export Department, 13 East 40th St., New York 16, N. Y., Cables "ARLAB" • aucliotape • • December INCLUDINC House & Garden Says • "Music In C. G. McProud, Editor and Publisher Harri e K. Richardson, Associate Editor Edgar M. Villchur, Contributin g Editor Luci Turner, Prp duction Manager S. L. Cahn, Advertising Director El izabeth Beebe, Circul ation Manager H. N. Reizes, Advertising Manager Life" Ed ar E. Newma Circulation Promoti on Director Ed itorial Advisory Board Representatives H. Thorpe Covington. Special Representative Howard A. Ch inn 677 N. Michigan Ave., Ch icago II , III . John D. Calvin Sanford R. Cowan. Mid-West Representati ve 67 W. 44th St., New York 18. N. Y. C. J. LeBel James C. Galloway. Pacific Coast Sales 816 W. 5th St., Los Angeles 17. Calif. J. p. Maxfield Technical Book & Magazine Co. 297 Swanston St., Melbourne. C. I. George M. Nixon Victoria. Australia CONTENTS OCTOBER, 1952 Vo l. 36, No. 10 Audio Patents- Richard H. Der! . ............. .... .... ......... 2 Letters . ... ..... ..... ... ... ........ ... ... ... .. .. .. .. ... 6 London Letter- Leollard Card'u,ner . .. ....... ..... ... .... 12 Book Reviews . .. ..... .... .. .............. .... ... ... .. .. 17 Says it l!!.. a big 24 page portfolio Editor's Report . .. ........ .. .... .. ... ... ... ....... ... ..... .. 18 Intermodulation Distortion- Richard C. H itchcock . .............. 21 packed with news and information A Critical Feedback Analysis- Harold Klimpel .. .. ..... .. .... ... 23 Stereophonic Reproduction- James Moil' ... ..... ..... ... ........ 26 on every phase of Music .' . Design for Clean Bass- Edwa1'd J. Gately, h. .. .............. 29 P lanning & Building a Radio Studio-Part 5- Eugene F. Co1'iell .. ....... 30 including feat ure articles A Corner-Mounting Infinite Baffie-M. V. Kiebe1't, h . .......... 32 The Vio l in~Pa1't 2- Alb'ert Preisrnan .... ........ .. ......... 34 on Tape Recorders, and H andbook of Sound Reproduction-Chapter 5- E . M. Villchlw . .. " . .... 36 High Fidelity. ~~~~':~~n~~ri;:~~e:~e~~ ' sic~ioN ' ... i ' ....... ..... ...... ....... .. .. .. 38 No Coded Signals- H. S . Mor1'·is .......... .. .... .. ... ... 40 Convention Progran1 .............. ... .... ....... ... ... 58 • Says it l.2. an important audience of Employment Register . ........ .. .. .. .. .. .. .......... .... ..... 83 influential readers who have the means to Record Revue-Edward Tatnal:l Ca,nby . .. .. ......... .. .. ......... 46 Tape Recorder Echo Effects- R. S. Houston .. ... ... .. ... .. .. .. 52 buy the best in mcUsical recording. Audio Fair Story ... .... .... .. ................ .. .......... .. 58 New Products .... .......... .. ........... .. ....... .. .. .. .... 62 • Says it .!£. your £fe alers in a special Some Pickup Design Considerations-Po G'. A . H. Voigt . ...... .. 64 promotion package complete with ideas Some Observations on Demonstration Technique- Harrie K. Richa1'dson . 84 New Literature ..... ..... ... ... ... ... ... ......... ........... 87 of how to increase business in Music {o r Price and Product Changes- Radio Master's Report . .. ..... .. 94 Christmas with House & Garden tie-ins. Industry Notes . .. .. .. .. ... .. .... .. .. ... ..... .. .. 95 Advertising Index ... .. ............ .. ...... .. ........ .... 96 • House & Gardm's December Music COVER Issue is quite evidently an ideal issue to Two prominent figures in the audio world combine to make this photograph one of the more newsworthy to grace }E's cover in many 1110nths. At the left is Mr. tzme in on. Music advertising in the issue Earl M. Johnson, newly-elected vice-president in ' charge of engineering and will be thoroug'hly merchandised. Tell station relations for Mutual Broadcasting System. On the right is Mr. R. your dealers to use the -issue itself as a Stahl, president of Ectro, Inc., Delaware, Ohio, explaining the design and operation of the new battery-operated Cub Corder tape recorder. selling mamtal ... as a part of holiday Mr. Stahl- who, incidentally, flew to New York solely for this displays. picture- made news of national impact recently when', as founder and president of Ciro, Inc., he ~o l d !uanufacturing rights for • Closing date fo r your the Ciroflex camera to Graflex Corporation, in order to de­ vote his future activities to the expanding field of tape advertisement in the December !·ecording. (Photo by Nemeth) M usic Issue is OCTOBER 15th. RADIO MAGAZINES, INC., P. O. BOX 629, MINEOLA, N. Y. AUDIO ENGINEERING (title registered U. S. Pat. OIT.) is published monthly at 10 McGovern Avenue. Lancaster. Po .• by Radio Magazln ... IDC .• Henry A. Scbober. President; C. G. McProud. Secretary. Executive and Editorial Offices: 20~ Front St .• Mineola. N. Y. Subscription rates-United Stat... U. S. Possessions and Can ad •• $3.00 for 1 year. $5.00 for 2 years; ellewbere $4.00 per year. Single copies 35c. Prlnted In U. S. A. All rights reserved. Entire contents House & Garden copyriebt 1952 by Radio Magazines, Inc. Entered as Second Class Matter February 9, 1950. at the Post Office. Lan· caster. Pa. under the Act of Marcb 3. 1879. 420 L exi~glon Avenue. New York 17. New York AUDIO ENGINEERING • OCTOBER, 1~52 NEW! • • ~l]1lDUCJ) • The turntable • • that YJll! helped • • • us design! [p~U'm!l~~ RICHARD H. DORP IVO POWER-AMPLIFIER CIRCUITS invented A (using the convention more common to , by Harry W. Becker of Chicago pro­ electronics that current flow and electron vide interesting possibilities for achiev­ How are identical) from plate to power ing high output and low distortion together supply. A t the same time the cathode cur­ with rather unusual economy of materials rent flows downward through winding B and size. from ground to cathode. The two windings The first is a single-tube output stage are thus in series aiding, with inverse volt­ with, according to the inventor, the advan­ age drop relations with respect to g round. tages of push-pull, negative feedback, and The latter is so because actual ground is low source impedance normally present only connected to the end of winding B nearest in much more elaborate circuits. The patent the center of the primary and a.c. ground is numbered 2,595,443 and the schematic is (we assume the power supply is conven­ REK-O-KUT shown in Fig. 1. tionally bypassed by its filte r ) is connected 3-SPEED, 16" The principal "gimmick" here is an out­ to the end of winding A nearest the center. put transformer with two primary windings T his is the same condition as occurs in an Transcription Turntable and extremely simple but ingenious cir­ ordinary push-pull stage. \;Yinding B, however, is the load element FOR BROADCAST AND cuitry in connection with it. T,he tube is a beam tetrode-pet'haps a 6L6 or something of a cathode follower. As such, the voltage RECORDING STUDIOS similar. The high end of the input signal is across it is in phase with the input voltage connected to the grid through blocking and the net voltage across it is the dif­ capacitor Ct in the usual manner and the ferential. The resulting feedback tends to other end of the input source may be reduce di stortion, as in any cathode fo l­ THE new B-16H three-speed, 16" tran­ ?,rounded. The lower end of grid-leak R" lower, and increase the effective input im­ scription turntable is not a modifica­ IS connected to the lower end of cathode­ pedance of the stage. Because of the mag­ tion of a two-speed machine, but a bias resistor R ., which is bypassed in the netic coupling with the plate winding A, c?mpletely new design, with opera­ usual way by C• . The junction of the two noise and distortion generated within the tIOnal controls suggested by leading resistors is not connected directly to ground, stage itself is reduced even further. engineers. Now you can play all three however, but through winding B of the So far the amplifier should give good re­ speeds-33'/3, 78 and the popular 45 transformer. Winding B is thus the load sults with enough excitation to produce -with equal facility. element of a conventional cathode-fo llower rated output. The output may be increased of the type in which the grid leak is usually well above normal rating, however, with­ The B-16H can be quickly and easily connected to a tap on a cathode res istor. out increase in distortion because of the fitted into your present 2-speed tran· s€reen current. Screen current is, as usual, scription consoles or cabinets. The base out of phase with plate current; that is, is drilled and tapped for mounting B+ when the grid goes positive and plate cur­ Audak, Grey or Pickering arms. Main· rent increases, screen current decreases.